1. Field of the Invention
The present invention is directed to certain improvements in the alkylation of aliphatic hydrocarbons in the presence of a fluorinated sulfonic acid catalyst.
More particularly, the invention is related to the recovery of the fluorinated sulfonic acid catalyst acid soluble oil (ASO) in the form of a tar from being formed as byproduct during alkylation of hydrocarbons.
2. Description of the Related Art
Acid catalyzed alkylation of aliphatic hydrocarbons with olefinic hydrocarbons is a well known process for the preparation of high octane gasoline products. Alkylation of aliphatic hydrocarbons is generally accomplished in the liquid phase by reacting paraffins and olefins in the presence of a strong acid catalyst.
Utilization of fluorinated sulfonic acids as efficient alkylation catalysts in the alkylation of aliphatic hydrocarbons with olefins, is disclosed in European Patent Application No. 433,954, which by reference is incorporated herein. By the disclosed process, a process stream including a hydrocarbon substrate and an olefinic alkylating agent is reacted by contact with the fluorinated sulfonic acid catalyst in a fixed bed alkylation reactor containing polar contact material. On the contact material is established a reaction zone with the fluorinated sulfonic acid catalyst adsorbed within a confined area of the contact material. In the reaction zone, the process stream is converted at alkylating conditions to a product stream of alkylated hydrocarbons by catalysis of the fluorinated sulfonic acid.
During the alkylation reaction, the acid catalyst and, consequently, the reaction zone moves as a well-defined band between the ends of the reactor due to interaction with the process stream flowing through and reacting in the zone.
During migration of the acid catalyst on the contact material, the catalytic activity of the fluorinated sulfonic acid is substantially retained and the acid is still catalytic active when the reaction zone reaches the reactor outlet.
Although it is possible to reuse the acid catalyst, as it reaches the outlet end of the alkylation reactor by reversing the flow direction of the process stream introduced into the alkylation reactor, small amounts of the acid catalyst will continuously be trapped in ASO byproduct being formed by side reactions during the process. The ASO adsorbs like the acid catalyst as a movable band on the support material adjacent to the reaction zone. It is, thus, possible to withdraw the ASO from the reactor, whenever it reaches one of the ends of the reactor.
Even if the ASO contains only small amounts of spent acid catalyst, it is desirable to recover the catalyst from the ASO in order to improve the economy of the alkylation process. Conventional methods, like distillation or extraction of the acid directly from the ASO, are not efficient because of strong interaction between the sulfonic acid and basic components in the tar.
It is, therefore, a principal object of this invention to provide a process for the efficient recovery of fluorinated sulfonic acid catalyst from an alkylation process.
In DK patent application No. 0287/93 a recovery process is disclosed, in which spent fluorinated sulfonic acid catalyst is regained by stepwise treating ASO from an alkylation process containing spent catalyst with a proton donating acid to convert the catalyst to its free acid form, and then removing the acid by stripping the tar with an inert stripping agent.
Spent fluorinated sulfonic acid catalyst may quantitatively be recovered by extracting the catalyst containing ASO with water. After extraction with water, it has been shown that the content of fluorinated sulfonic acid catalyst in the extracted ASO is below one ppm. Extracted acid catalyst can be recovered from the aqueous solution by neutralization with a base, and, subsequently, protonization in sulfuric acid and distillation of the acid.
A substantial quantitative recovery is thereby provided.
The above process provides an efficient recovery of valuable fluorinated sulfonic acid catalyst. The recovery of the acid after neutralization with a base, however, represents certain problems; thus, a number of steps in the further treatment of the obtained salt from the neutralization step, in particular, drying of the salt, complicates the recovery process and diminishes the overall process economy.